1. Field of the Invention
Embodiments of the invention relate to a solar cell and a solar cell module.
2. Description of the Related Art
Recently, as existing energy sources such as petroleum and coal are expected to be depleted, interests in alternative energy sources for replacing the existing energy sources are increasing. Among the alternative energy sources, solar cells have been particularly spotlighted because, as cells for generating electric energy from solar energy, the solar cells are able to draw energy from an abundant source and do not cause environmental pollution.
A solar cell generally includes a substrate and an emitter layer, each of which is formed of a semiconductor, and electrodes respectively formed on the substrate and the emitter layer. The semiconductors forming the substrate and the emitter layer have different conductive types, such as a p-type and an n-type. A p-n junction is formed at an interface between the substrate and the emitter layer.
When light is incident on the solar cell, a plurality of electron-hole pairs are generated in the semiconductors. The electron-hole pairs are separated into electrons and holes by the photovoltaic effect. Thus, the separated electrons move to the n-type semiconductor (e.g., the emitter layer) and the separated holes move to the p-type semiconductor (e.g., the substrate), and then the electrons and holes are collected by the electrodes electrically connected to the emitter layer and the substrate, respectively. The electrodes are connected to each other using electric wires to thereby obtain electric power.
At least one current collector, such as a bus bar, is positioned on each of the emitter layer and the substrate, and the current collector on the emitter layer is connected to the electrode electrically connected to the emitter layer and the current collector on the substrate is connected to the electrode electrically connected to the substrate. Thus, the electrons and the holes collected by the corresponding electrodes of the emitter layer and the substrate move to a load connected to the outside through the corresponding current collectors.
However, in this case, because the current collectors are formed on the emitter layer on an incident surface of the substrate, on which light is incident, as well as a non-incident surface of the substrate, on which light is not incident, an incident area of light decreases. Hence, efficiency of the solar cell is reduced.
Accordingly, a metal wrap through (MWT) solar cell and a back contact solar cell were developed so as to prevent a reduction in the efficiency of the solar cell resulting from the current collectors. In the MWT solar cell, a current collector connected to an emitter layer is formed on a back surface of a substrate opposite a light incident surface of the substrate. In the back contact solar cell, all of electrodes collecting electrons and holes are formed on a back surface of a substrate.
A solar cell module is manufactured by connecting a plurality of solar cells each having the above-described structure to one another. An electrical connection between the plurality of solar cells is completed by connecting current collectors of the plurality of solar cells in parallel or in series to one another using a connector.